In sensor network systems, changes in the environment of an area where a large number of wireless sensor nodes are disposed are detected by the sensor nodes. A related technique of transmitting data to a sensor node that is not directly connected to by relay transfer via multihop communication among sensor nodes is known.
According to another technique, a wireless node sets an internal clock by a synchronization signal transmitted from a host and switches a power saving mode and a regular mode (for example, refer to Japanese Laid-Open Patent Publication No. 2008-306657).
A further technique is known where in remote measuring, a portable receiver uses a timer and based on a synchronization message transmitted from a remote transmitter, measures the time until the next message is received. Further, when reception is to be performed, power supply to a receiver that is OFF is turned ON and the receiver is operated (for example, refer to Published Japanese-Translation of PCT Application, Publication No. 2007-515863).
According to another known technique, a wireless sensor uses a clock time received from a high order station and corrects time deviations at the wireless sensor after a sufficient period of time has elapsed since powering on. The wireless sensor further reflects the corrections on the driving time of the wireless sensor (for example, refer to Japanese Laid-Open Patent Publication No. 2005-348186).
According to another known technique, at a remote controller receiver, signal standby is performed intermittently whereby a reduction of power consumption for signal standby can be facilitated, enabling battery life to be extended (for example, refer to Japanese Laid-Open Patent Publication No. H5-292564).
Nonetheless, conventionally, in a system where communications nodes receive a synchronization signal transmitted from a communications apparatus that aggregates data of the communications nodes and the timing when the synchronization signal is transmitted is unknown, the communications nodes remain in reception standby continuously for long periods of time, arising in a problem that the capacity of the battery of the communications nodes has to be large.